1. Field of the Invention
The present invention relates to a television camera, and more particularly, to an adjustment of a detected video signal balance (highlight balance, gamma balance, grayscale first-level balance, and dark balance, etc.).
2. Description of the Related Art
One example of an adjustment of a detected video signal balance in a conventional television camera will be described with reference to FIGS. 1, 2, and 4. The detected video signal balance indicates a highlight balance (white balance), gamma balance, grayscale first-level balance (flare balance), and dark balance (black balance), etc.
As described in Japanese Patent Application Laid-Open Publication No. 2011-4239, for example, the conventional television camera needs a grayscale chart in order to satisfactorily capture a subject, when the detected video signal balance is automatically adjusted.
FIG. 1 is a block diagram illustrating a configuration of the conventional television camera. 100 denotes a television camera, 101 denotes a camera head, 102 denotes an optical system such as a lens, 103 denotes a camera control unit, 104 denotes a waveform monitor, 105 denotes a monitor, 106 denotes a remote controller, 107 denotes a camera cable, 108 denotes a remote-controller cable, 110 denotes a viewfinder mounted to the camera head 101, and 121 denotes a grayscale chart set as a subject.
FIG. 2 is a view for schematically describing the grayscale chart. In the grayscale chart illustrated in FIG. 2, a leftmost chart in an upper line is black, a rightmost chart in the upper line is white, a leftmost chart in a lower line is white, and a rightmost chart in the lower line is black. The level of the grayscale between black and white is schematically illustrated by density of horizontal lines. 200 denotes a displayed image of the grayscale chart 121 captured by the television camera 100, 201 to 206 denote frame-like detection gates (the horizontal lines in each frame are not illustrated), and 251 to 253 denote scanning lines. The displayed image 200 in FIG. 2 is displayed on a display unit of a video image display apparatus, such as the viewfinder 110, the monitor 105, and the waveform monitor 104. Therefore, an operator can carry out an adjustment of a field angle for adjusting the detected video signal balance on any one of the video display apparatuses.
FIG. 4 is a view (waveform signal chart) illustrating an image 400 of signal levels of video signals on the scanning lines 251, 252, and 253 in the displayed image 200 of the grayscale chart in FIG. 2, the image 400 being displayed on the video image display apparatus such as the viewfinder 110, the monitor 105, and the waveform monitor 104, etc. A video image signal level 250s is obtained by one scanning line (the scanning line 251, 252, or 253, or another scanning line) under the condition in which a lens iris of the optical system 102 is closed to block incident light. A video image signal level 251s is a video image signal level of the scanning line 251. A video image signal level 252s is a video image signal level of the scanning line 252. A video image signal level 253s is a video image signal level of the scanning line 253. A signal level enclosed by a dashed ellipse 41 is a level (detection level 41) of the video image signal of the detection gate 204. A signal level enclosed by a dashed ellipse 42 is a level (detection level 42) of the video image signal of the detection gate 205. A signal level enclosed by a dashed ellipse 43 is a level (detection level 43) of the video image signal of the detection gate 206. A signal level enclosed by a dashed ellipse 43′ is a level (detection level 43′) of the video image signal of the detection gate 201. A signal level enclosed by a dashed ellipse 42′ is a level (detection level 42′) of the video image signal of the detection gate 202. A signal level enclosed by a dashed ellipse 41′ is a level (detection level 41′) of the video image signal of the detection gate 203. A signal level enclosed by a dashed ellipse 44 is a detection level 44. FIG. 4 illustrates the signal levels of the respective scanning lines between n1 and n2 in FIG. 2. In FIG. 4, the detection level 42 and the detection level 42′ are equal to each other, since they have already been adjusted.
In FIG. 1, the television camera 100 firstly captures the grayscale chart 121, and adjusts the field angle by using the detection gates 201 to 206 as a reference. An operator such as a cameraman sees the displayed image illustrated in FIG. 2, and manually adjusts the field angle. The frame-like detection gates 201 to 206 for the adjustment of the field angle set beforehand for the video image display apparatus are superimposed on the displayed image 200.
After the adjustment of the field angle, a control unit, including a CPU and FPGA, of the conventional television camera automatically adjusts an input/output characteristic of RGB signals in order that a black level, a white level, a flare level, and a gamma level, etc. of each video image signal in the detection gate area in the captured grayscale chart 200 assume respective predetermined set values.
Specifically, the operator adjusts the field angle of the television camera 100 in order that each of the detection gates 201 to 206 is superimposed on a specific portion of the displayed image 200 of the grayscale chart in FIG. 2. The operator adjusts the field angle by manually operating the imaging position of the camera, or the zoom/focus position of the lens.
The detection gates 201 to 206 for the adjustment of the field angle are superimposed only on a picture output from the video image display apparatus or the camera control unit 103, not superimposed on a signal of a main line. The signal level of the video image signal in the area in the detection gates 201 to 206 is detected, whereby the automatic adjustment of the detected video image signal balance is performed by the control unit including the CPU.
The television camera 100 conventionally captures the grayscale chart 200 as a reference subject, and adjusts its signal level in order to automatically adjust the detected video image signal balance. With this process, the television camera 100 adjusts the respective balances.
As described above, the operator adjusts the field angle such that each of the detection gates 201 to 206 is superimposed on each grayscale of the grayscale chart 200, and then, starts the automatic adjustment.
The automatic adjustment is carried out by the procedure described below.
(a) The lens iris of the optical system 102 is closed to block the incident light. Then, the signal level in the dark balance is adjusted by the detection level 44, and is converged with an adjusted value. Alternatively, the light incident on the optical system 102 may be blocked by using an optical filter.
(b) The lens iris is automatically adjusted in order that a level of a G signal (detection level 41′, and detection level 41) at the detection gates 203 and 204 upon capturing the grayscale chart 200 becomes a detection level of 100% rated level of the video image signal for the highlight balance adjustment. The R and B signals are adjusted to be converged with adjusted values with respect to the G signal. As a result, the highlight balance is adjusted on the detection gates 203 and 204.
(c) With the lens iris adjusted in (b), the levels of the R, G, and B signals are adjusted in order that the level (detection level 43′, and detection level 43) of each of the R, G, and B signals becomes a detection level of 12% of the rated level of the video image signal on the detection gates 201 and 206 upon capturing the grayscale chart 200. The levels of the R, G, and B signals are adjusted to be converged with the adjusted values. As a result, the grayscale first-level balance is adjusted.
(d) With the lens iris adjusted in (b), the levels of the R, G, and B signals are adjusted in order that the level (detection level 42′, and detection level 42) of each of the R, G, and B signals becomes a detection level of 58% of the rated level of the video image signal on the detection gates 202 and 205 upon capturing the grayscale chart 200. The levels of the R, G, and B signals are adjusted to be converged with the adjusted values. As a result, the gamma balance is adjusted.
(e) The convergence with the adjusted value of each balance in the procedures (b), (c), and (d) is repeated several times.
(f) Again, the lens iris is closed to block the incident light, and then, the dark balance is adjusted with the detection level 44, and the signal levels are converged with the adjusted value.